---
title: Prune pre-merge history
sidebar_position: 9
description: Reduce the size of your database by removing pre-merge blocks from your blockchain
---

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Node operators using [Snap sync](../concepts/node-sync.md#snap-synchronization) can significantly reduce
disk usage by removing [pre-merge](https://ethereum.org/en/roadmap/merge/) Proof of Work (PoW)
block data from the local database.

Besu can prune all pre-merge block bodies and associated transaction receipts, leaving only headers and
the genesis block.

:::warning

Besu does not currently provide a way to import pre-merge block data after pruning.
If you need to restore the full pre-merge history, you can revert to the former Snap sync behaviour and download
all blocks from peers by setting
[`--snapsync-synchronizer-pre-checkpoint-headers-only-enabled=false`](../reference/cli/options.md#snapsync-synchronizer-pre-checkpoint-headers-only-enabled).

:::

Besu provides multiple options to prune the historical blockchain data:
- [Offline pruning](#offline-pruning) to prune data on a stopped Besu instance.
- [Online pruning](#online-pruning) to prune data on a running Besu instance.
- [Sync Besu](#sync-without-pre-merge-blocks) using Snap sync, which by default prunes the historical
    blockchain data.

## Offline pruning

The fastest option for pruning pre-merge blocks is to perform an offline prune. It won't prune as much data as a full resync.

1. Ensure your Besu instance has stopped, and run the following command:

    ```bash
    besu --data-path=/path/to/your/database storage prune-pre-merge-blocks
    ```
    The command [`prune-pre-merge-blocks`](../reference/cli/subcommands.md#prune-pre-merge-blocks)
    prunes the database using the default options.

    On completion, you'll receive the `Pruning pre-merge blocks and transaction receipts completed` log message.
    It should only take a few minutes to complete but has been known to take up to two hours on occasion.

1. Add the following RocksDB garbage collection options and restart Besu to help free up space:

   - `--Xplugin-rocksdb-blockchain-blob-garbage-collection-enabled`
   - `--Xplugin-rocksdb-blob-garbage-collection-age-cutoff=0.5`: The fraction of file age that makes a blob file eligible for garbage collection; `0.5` means only the oldest 50% of files are eligible.
   - `--Xplugin-rocksdb-blob-garbage-collection-force-threshold=0.1`: The fraction of garbage within an eligible blob file required to trigger compaction; `0.1` triggers garbage collection when at least 10% of an eligible file's content is garbage.

   :::info
   In testing, we saw the space increased by up to 200GB before the space was finally reclaimed.
   We suggest waiting 24-48 hours for all the space to be reclaimed.
   :::

1. (Optional) Remove the RocksDB options and restart Besu. This will disable garbage collection which isn't necessary after pruning has reclaimed all the space.

## Online pruning

:::caution Deprecated

Online pruning using `--history-expiry-prune` is deprecated in Besu version 26.1.0 and will be removed in a future release.
Use [offline pruning](#offline-pruning) or [sync without pre-merge blocks](#sync-without-pre-merge-blocks) instead.

:::

Online pruning allows you to prune the pre-merge blocks on a running Besu instance. It has the least
downtime but may impact normal operations for lower spec users. Add the [`--history-expiry-prune`](../reference/cli/options.md#history-expiry-prune) option and restart your Besu node.

:::note
The early access option `--Xpre-merge-pruning-quantity` can be used to specify how many blocks to prune
for each new block added to the chain. For example, `--Xpre-merge-pruning-quantity=10`.
During testing on a 4 CPU machine, we only noticed an impact to Besu when this was tuned to `1000`
:::

The Besu logs will print the progress in the logs, and you'll see the `Done pruning pre-merge blocks.` message
when complete.

## Sync without pre-merge blocks

This option has the most downtime but reclaims the most disk space.
Delete your database and by default, syncing a Besu node using [`SNAP` sync (`--sync-mode=SNAP`)](../reference/cli/options.md#sync-mode)
will prune pre-merge blocks and only retain their headers.

If you're a solo staker, consider using [RocketPool's rescue node](https://rescuenode.com/docs/about)
to minimize downtime.